This project will accomplish six goals: 1) estimation of the relative contributions of environmental and genetic factors to individual differences in quantity and frequency of alcohol intake; 2) estimation of the relative contributions of environmental and genetic factors to differences in response to alcohol; 3) study of the effects of such variables as drinking history, family history of alcoholism, and baseline electrophysiological characteristics on response to alcohol; 4) validation of alcohol consumption estimates obtained with the Substance Use Questionnaire, a retrospective self-report of drug use; 5) elucidation of the effects of alcohol on certain electrophysiological parameters; and 6) description of alcohol use and response to alcohol in a well-established sample of twins who can be followed as they move through the period of risk for alcoholism. Twin pairs from the Minnesota Twin Study and the Minnesota Twin Registry will participate in three phases of the project. First, variability in alcohol intake will be investigated. Each twin (MZ=100 and DZ=100 pairs) will complete the Substance Use Questionnaire (SUQ), a 128-item drug use history. Then, each twin will keep a record of his alcohol consumption for 28 days using the Drinking Diary, a standard form used in this laboratory. Finally, variability in response to alcohol will be studied in 80 pairs (MZ=40 and DZ=40 pairs). Each twin will report to the laboratory for two 4.5-hour sessions. In one session, he will receive a placebo and in one he will receive 1.24 ml/kg alcohol. The 70-minute test battery, which includes variables previously demonstrated to be reliable indicators of alcohol effects, will be administered once before and twice (0 and 70 minutes) after alcohol ingestion. Parameters of the resting electroencephalogram (EEG) and the visual evoked potential (VEP) will be assessed as will a set of behavioral measures. Comparison of intrapair similarity for MZ and DZ pairs will permit estimation of the relative contributions of genetic and environmental factors to individual differences in patterns of alcohol-drinking and in response to alcohol. Attention to "special cases" (e.g., twins with a family history of alcoholism, MZ pairs discordant for drinking history) will allow examination of the effects of these variables in explaining variability in response to alcohol. Creation of a data base including questionnaire and laboratory results will provide valuable data for future prospective studies of the twins as they pass through the age of risk for alcoholism.